Semiconductor elements used in a central processing unit (CPU) or the like are electrically connected and fixed to a substrate in a semiconductor. The temperature of a semiconductor element rises when the semiconductor element is operated. Thus, the temperature of the semiconductor element has to be forcibly lowered. Otherwise, the semiconductor element may not be able to operate at full capacity. Hence, to improve the heat dissipation property of a semiconductor element, a heat radiation component (for example, a metal heat radiation plate) that releases the heat emitted from a semiconductor element into atmosphere may be arranged on a semiconductor element. This forms a path through which the heat emitted from a semiconductor element is externally released. In this case, a thermal interface material (TIM) is arranged between the semiconductor element and the heat radiation plate. The thermal interface material absorbs the unevenness in the surfaces of the semiconductor element and the heat radiation plate and thereby decreases the contact thermal resistance therebetween. By using the thermal interface material, heat is smoothly conducted from the semiconductor element to the heat radiation plate. Japanese Laid-Open Patent Publication Nos. 2003-037228 and 11-068360 describe examples of thermal interface materials.
FIG. 18A illustrates one example of a semiconductor device 100. A semiconductor element 120 is arranged on a wiring board 110. A heat radiation plate 130 is thermally coupled to a rear surface of the semiconductor element 120. The heat radiation plate 130 includes a recess 131 that accommodates the semiconductor element 120. The recess 131 includes a bottom surface 131A joined with the semiconductor element 120 by a thermal interface material 140. The thermal interface material 140 transfers heat from the semiconductor element 120 to the heat radiation plate 130 to prevent the temperature of the semiconductor element 120 from rising.
The thermal interface material 140 may be formed from an organic resin binder having a low elastic modulus and containing fillers of an inorganic material (e.g., silica, alumina, or boron nitride) having a higher thermal conductivity than an organic material or of a metal material (e.g., silver, copper, or nickel).